The research of the McArdle Laboratory for Cancer Research is divided into three broad categories: Biochemical Studies in Chemical Carcinogenesis, Molecular Biology and Genetics of Tumor Viruses, and The Cell Cycle and Differentiation in Tumor Biology. The chemical carcinogenesis program encompasses a broad fundamental a approach to the chemistry, biochemistry, and biology of mutation, tumor initiation, and tumor promotion due to chemicals. These projects include studies on the genetic control of initiation and promotion, the biochemical regulation of enzyme activities, the metabolic activation of carcinogens, the characterization of cellular receptors for tumor promoters, and the analysis of preneoplastic lesions. The studies in tumor virology encompass the molecular biology and genetics of avian and murine RNA tumor viruses and of three primate DNA tumor viruses, simian virus 40, papillomaviruses, and Epstein-Barr virus. This tumor virology program approaches problems of the identification of viral genes responsible for cancer, their mechanisms of transformation and control of tissue specificity, the mechanisms of integration or maintenance of viral genomes, the control of expression of viral genes, and the con- struction and properties of vectors based on tumor viruses. The tumor biology program is a multidisciplinary approach to the elucidation of regulatory mechanisms that influence the growth, replication, and differentiation of normal and cancer cells. For instance, this program examines factors affecting the transcription of specific genes and the role of RNA structure in its intracellular-localization, stability, and expres- sion. The importance of cell membranes for cell replication control and immune recognition, as well as for the regulation of cell differentiation, are being investigated in a range of eukaryotic systems. Integral to the objectives and aims of the McArdle Laboratory is research training at the pre- and postdoctoral levels in the general area of the cell and molecular biology of neoplasia and carcinogenesis. Approximately 100 individuals are presently receiving such training in the McArdle Laboratory, and more than 700 have received research training in these areas in the McArdle Laboratory in the past.